First of all have you thought about a private sale? Or an auction?
Your trader car came from the auction, they leave it an their lot, add about £1,500 and sell it to you with a bit of a shady warranty. Why line their pockets.
Due diligence old boy, take your time and don't be impatient. Once you find a car you like you can line up your insurance so it is a phone call away. Your tax is online, easy.
AT have a superb bit of info here:
http://www.autotrader.co.uk/advice/2014/02/buying/buying-a-used-car
Once you have handed over your wedge all the cars problems belong to you - try to spot them and knock off the cash to sort them out.
Have a look underneath - rusty exhaust?
Things hanging down
Ideally see the car started from cold
Move it forward - any oil patch?
Any tyres need replacing - the can be £80 each
Any alloys need refurbing - £80 each
Hard to check the suspension but bounce it and listen during the test drive
Look at all the paintwork - any dings - rust - poorly fitting panels - has it been bumped/repaired - best place to look is under the bonnet and at the spare wheel well
Spare ok?
Headlights fogged?
Windscreen glass ok - any cracks
Feel the carpets - any damp in the foot wells?
Check ever single electric thing works - windows, mirrors, s/roof, make sure the AC blows frosty air (£80 to have it recharged and much more if it is broken)
Are the two working keys - see them work - if there is one knock off the cost of a new key (this can be £200 to £250!)
Side and centre mirrors ok?
Radio working, take a cd with you
Engine - have a look under the oil cap - look clean?
Oil look ok?
Is the engine bay full of leaves and uncared for?
Test drive, I often let them drive if it is a private sale - go on a good 20-minute journey - see it warm up to temperature correctly - listen - should be smooth - gear changes smooth.
Look through the service history - verify the mileage with the MOT's
Has it been serviced each year?
When is the next service?
When was the cam belt/water pump changed? (costs about £350 and every 3 years with VW)
I like petrol, I have a 3 door 1.4 2002 Mark 4, bodywork is amazing on them lasts forever - plus some enthusiast will always buy these off you.
Try to buy one off an older mature person, preferably a little old lady. Let us know how you get on - exciting!
What Car? I like German cars, focus is good don't know anything about them, I personally like
3 dr VW golf petrols